1. Field of the Invention
The present invention relates to a device for reducing the load imposed on an internal combustion engine when it is started, and more particularly to a device for reducing the starting load on an internal combustion engine by automatically opening an intake valve or an exhaust valve thereof slightly to lower a compressive pressure in the combustion chamber, thereby reducing the starting load on the engine, the device being operable to automatically cancel the action to lower the compression in the combustion chamber when the engine operates normally.
2. Prior Art
One known device for reducing the starting load on an internal combustion engine is disclosed in Japanese Utility Model Publication No. 63(1988)-2565, for example. The disclosed device includes a camshaft which has a cam for pushing a valve tappet in sliding contact therewith, and a tappet pusher lever angularly movably mounted on the camshaft. A weight which partly engages the tappet pusher lever is swingably mounted on a side of a gear wheel which is coaxially mounted on the camshaft. The weight is normally urged toward the camshaft by a coil spring which has one end coupled to a pin fixed to the side of the gear wheel. When the internal combustion engine rotates at a low speed, the tappet pusher lever engaging the weight is caused to project out of the base circle of the cam under the bias of the coil spring, and pushes the tappet upwardly, thereby automatically opening an intake or exhaust valve slightly. Therefore, the compressive pressure in the combustion chamber is lowered to reduce the load on the engine when it is started. When the rotational speed of the engine reaches a normal speed, the weight is subjected to a centrifugal force which counteracts the bias of the coil spring, and therefore swings outwardly away from the camshaft. The tappet pusher lever, which is engaged by the weight, is also angularly moved into the base circle of the cam, whereupon the automatic opening of the intake or exhaust valve in the low-speed rotation of the engine is canceled.
Some recent internal combustion engines include camshafts molded of synthetic resin for reduced weight. If the known device for reducing the starting load on an internal combustion engine is incorporated in such an internal combustion engine with a camshaft molded of synthetic resin, the molded camshaft and the gear wheel are drilled or pins are mounted on them, with the weight and other components being supported by the drilled holes or pins.
Since it is necessary to drill the molded camshaft or fix pins to the molded camshaft for the attachment of the weight and other components, the camshaft is reduced in mechanical strength, and it is laborious and time-consuming to install the camshaft in place.